Inspectioneering
Inspectioneering Journal

Pendulum Effect: Part 1

By Del Underwood at Det Norske Veritas. This article appears in the January/February 1997 issue of Inspectioneering Journal
1
Likes
This article is part 1 of a 3-part series.
Part 1 | Part 2 | Part 3

 

Back before I became a consultant in 1962, I was employed by TransCo. My boss had a number of very descriptive expressions for commonly encountered problem conditions with reciprocating compressors. One of them that I have always appreciated over the previous 30 plus years was his term for pendulum action of a large unsupported mass on the end of a vibrating pipe. He called it "a billiard ball on the end of a fly rod". You avid fisherman will appreciate that one.

The most common pendulum configuration, i.e., billiard ball on a fly rod, encountered in plant design is that shown in Figure 1. Here, a heavy valve has been installed on the end of a small diameter nipple which is welded into the side of a flow line. This practice dates back many years and is still incorporated in plant design drawings, which have never been updated in this respect. It is a design which has very little tolerance for vibration. The heavy mass (the valve) overswings from the vibration in the pipe, creating amplified cyclic stresses in the weld between the nipple and the flow line. Under what would ordinarily be considered reasonable vibration conditions, this nipple will eventually fail.

This content is available to registered users and subscribers

Register today to unlock this article for free.

Create your free account and get access to:

  • Unlock one premium article of your choosing per month
  • Exclusive online content, videos, and downloads
  • Insightful and actionable webinars
GET STARTED
Interested in unlimited access? VIEW OUR SUBSCRIPTION OPTIONS

Current subscribers and registered users can log in now.


Comments and Discussion

There are no comments yet.

Add a Comment

Please log in or register to participate in comments and discussions.


Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Job Postings

Discover job opportunities that match your skillset.

Case Studies

Learn from the experience of others in the industry.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.

Blog

Read short articles and insights authored by industry experts.

Acronyms

Commonly used asset integrity management and inspection acronyms.

Downloads

Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

Videos

Watch educational and informative videos directly related to your profession.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.